home screen: "start new" behaviour not reset if non-<alt> modifier active while releasing <alt>

[sascha_silbe]

Steps to reproduce:

1. Enter home screen (ring layout)
2. Press and hold <alt>
3. Press and hold <shift>
4. Release <alt>
5. Release <shift>
6. optional: click on any activity icon that was previously colored (i.e. has existing sessions in the Journal)

What I expected:
Either don't change behaviour at all if <shift> is active (in addition to <alt>) or reset the state once <alt> has been released.

What happened:
"Start new" behaviour was "stuck", i.e. activity icons remained uncolored (even after releasing <shift>) and after clicking on one of them a new instance is started (instead of resuming an existing one).

[sascha_silbe]

Still happens.

[carrott]

I see this on Sugar 0.98.7 on XO-system 1a for XO-4 (build 49) when following the steps to reproduce in the description. I see this most often when I use alt-tab to switch applications, in this case you can release tab before alt and when you switch back to the activity ring, none of the activities are coloured.

[Sam Parkinson]

Fix weirdness with pressing SHIFT & ALT on the home screen - fixes #1490

Changeset: 58d8588d3d12328ce6e87bf65e91c4d640fdda37